A tape recorder includes a magnetic head, a switch connected to a power supply for applying a predetermined voltage to the magnetic head, and a current control circuit for controlling the amount of current flowing through the magnetic head.
The current control circuit includes a p-MOSFET connected at a drain to a first node, at a gate to an input terminal and at a source to a power supply, an n-MOSFET connected at a drain to the first node, at a gate to the input terminal and at a source to ground, an n-MOSFET connected at a drain to an output terminal, at a gate to a second node and at a source to ground, a resistor connected between the first node and the second node, and a capacitor connected between the second node and ground.
In operation, when the switch is turned on or off, current flowing through the magnetic head is rapidly changed to be increased or decreased between zero level and the maximum level, so that the magnetic field change occurs in the magnetic head to record the change into a magnetic tape. On the other hand, the current is gradually changed to be increased or decreased between the maximum level and zero level by controlling of the current controller, so that magnetic data is recorded from the magnetic head into the magnetic tape. That is, digital data having a level corresponding to a changing rate of the current flowing through the magnetic head is recorded on the magnetic tape.
In a reproducing mode, a reproducing circuit has positive and negative threshold levels for detecting a recorded data. The positive and negative threshold levels are set to be intermediate values between high level data and low level data on the positive and negative sides, respectively. The magnetic head detects the magnetic data of the magnetic tape which is then compared with the threshold levels in the reproducing circuit.
According to the conventional current control circuit, however there are disadvantages in that the threshold levels of the magnetic data reproduction are different between the positive and negative sides, because the absolute values of the low level data are different between the positive and negative sides because the changing rates of currents flowing through the magnetic head are different between the positive and negative sides due to a circuit structure of the current controller. This will be explained in more detail later. Therefore, noise margins become different between the positive and negative sides, so that operation of the magnetic data reproduction is unstable. Further, the reproducing circuit must be provided with two different detectors each having a different threshold level for detecting a corresponding side of positive and negative levels, so that the structure of the reproducing circuit including the magnetic head becomes complicated.
Otherwise, it is possible that the threshold levels of the magnetic head are set to be the same level, if a resistance of a resistor and a capacitance of a capacitor are set to be sufficiently high in the current controller to equalize the current changing rates on the positive and negative sides. However, a large space is necessary for the large resistor and the large capacitor, so that the current control circuit is difficult to be fabricated compactly.